Synthesis And Research Of Hydroxide Composites In Situ Derived From Phosphate Compounds For Supercapacitor

Due to the rapid climate change,humanity,solving the problem of atmospheric pollution,is on the path of transition from energy obtained from the combustion of hydrocarbons to alternative energy sources.But the instability of the energy received from the sun and wind determines the search for systems for the correct use and storage of such energy.In this regard,the need for power supplies of high energy,power and increased resource is constantly growing,therefore,research on the modification and development of electrode materials for supercapacitors is a priority in the world energy industry.This study examines promising cathode materials based on nickel and cobalt phosphates,which in alkaline media are transformed into electroactive forms of hydroxides,which have a high capacity and good stability for a long time.Herein,various phosphate compounds of nickel and cobalt were obtained,and anode materials such as highly porous carbon and bismuth-based composite were successfully synthesized to create a full-fledged supercapacitor.The studies carried out were as follows:1)Ni₂P₂O₇,Co₂P₂O₇ and Ni-CoP₂O₇ in situ delivered hydroxide materials in alkaline electrolyte as cathodes for supercapacitor.Here is a strategy for the preparation of active nanoforms of hydroxides using Ni₂P₂O₇,Co₂P₂O₇ and Ni-CoP₂O₇,which were obtained by a simple method of precipitation in aqueous solutions.These phosphates are then converted in situ to hydroxide materials in an alkaline electrolyte（6M KOH）as cathodes for the supercapacitor.The resulting electrode materials were studied in detail using XRD,SEM,FTIR and XPS.When nickel and cobalt are combined,the effect of synergy of electrochemical properties is observed.Overall,（Ni-Co）（OH）₂provided a high specific capacitance of 1097 F·g^-1compared to Ni（OH）₂(684 F·g^-1)and Co（OH）₂(276 F·g^-1).The cyclic life of Ni-Co（OH）₂ materials is also measured and the capacitance only declines 3.7%after1000 cycles.2)In situ transformation of Na₄Co₃P₄O₁₅ to Co（OH）₂ nanoforms and highly porous carbon for aqueous supercapacitor using redox additive electrolyte.We consider a strategy to improve the basic characteristics of asymmetric supercapacitors by sequentially modifying electrode materials and electrolyte.The cathode was fabricated by converting Na₄Co₃P₄O₁₅ phosphate in situ to the Co（OH）₂ nanoform in an alkaline electrolyte.The resulting electrode materials were studied in detail using XRD,SEM,TEM,FTIR,Raman,XPS and BET.Electrochemical tests have shown additional possibilities to increase the specific capacity of electrodes using a combined alkaline electrolyte 1M KOH+0.1M K₃[Fe（CN）₆].Low-cost commercial carbon was used as the initial anode material,which has been subsequently activated by KOH at 850°C under an Ar atmosphere.Additionally,this treatment has allowed to increase the porosity and surface area of carbon from 937.2 to 1441.2 m²·g^-1,and electrochemical capacity from 58 to 101.2 F·g^-1.The assembled asymmetric supercapacitor demonstrates a significant specific energy of 42 W·h·kg^-1 with a power density of 400 W·kg^-1 and has a good stability of cycle life（retains more than 93%capacity after 1500 charge-discharge cycles）.The obtained results show that in a future the proposed technological routes can improve supercapacitors in the energy sector.3)Ni（OH）₂ nanocomposites in situ derived from Na₄Ni₃（PO₄）₂P₂O₇ and Bi（nanoparticles）/CNx（nanosheets）nanocomposites for a high performance aqueous hybrid supercapacitor.The evolution of high-performance and stable electrode materials for supercapacitors plays a vital role in the next generation of energy storage devices.Nano-Na₄Ni₃P₄O₁₅ was synthesized by water deposition with subsequent annealing of the precipitate.The resulting Ni（OH）₂ electrode material in situ derived from Nano-Na₄Ni₃P₄O₁₅ in 6M KOH,and tested as cathode material which delivered a maximum specific capacitance of 545 F·g^-1 at 0.5 A·g^-1 current density.Furthermore,Ni（OH）₂ show a good cyclic stability about 85.5%retention of its initial capacitance up to 5000 cycles at the current density 1 A·g^-1.In addition,we present a simple method for preparing Bi（nanoparticles）/CNx（nanosheets）nanocomposites as electrode materials for supercapacitors,which were synthesized by thermally treating bismuth citrate and urea at 550–700°C under an Ar atmosphere.According to physicochemical studies（XRD,SEM,TG-DTA,XPS,FTIR,and BET）,a“smeared”bismuth formation or the formation of nanoparticles on the CNx surface of interwoven 2D-nanosheets at different calcination temperatures was observed.Electrochemical measurements show that the specific capacity of the composites can reach 1251 F·g^-1（more than 90%of the theoretical value）at a current density of 500m A·g^-1 in a 6M KOH electrolyte,and most two-dimensional CNx-based nanostructures remain intact after multiple galvanostatic charge–discharge processes,which is promising for the development of highly efficient supercapacitors.A supercapacitor composed of Bi/CNx nanocomposites for the negative electrode and Ni-layered hydroxide for the positive electrode demonstrates a high energy density of58 W h·kg^-1 with a power density of 800 W·kg^-1 accompanied by a good cycle life（the parameters decreased down to only 78%after 1000 charge–discharge cycles）.Our current results indicate that the addition of urea not only determines the morphology of the composites,but also lays the foundation for the development of new types of nanocomposites for the power industry.In summary,strategies for the in situ production of electrochemically active oxides of nickel and cobalt hydroxides from phosphate precursors have been improved.The synergism of properties was shown when using mixed nickel-cobalt phosphates,and the success of this path was confirmed by examples of assembled supercapacitors.